Method of forming optical wedges on lenses and reflectors



Patented Dec. 30, 1947 UNITED STATES PATENT OFFICE METHOD OF FORMINGOPTICAL WEDGES N LENSES AND REFLECTORS 2 Claims. (of. 117-106) Thisinvention relates to optics, and more particularly to lenses orreflectors having curved surfaces.

This application is a division of an application filed October '7, 1941,under Serial No. 413,964, in the name of Thomas W. Sukumlyn, andentitled, Optical means, since issued as Patent No. 2,341,827 onFebruary 15, 1944.

Lenses and reflectors are of course utilized for altering the directionsof light rays, respectively by refraction and reflection. Such devicesmay be generically referred to as optical units, and this term as usedhereinafter will be utilized to include both lenses and mirrors orreflectors.

When the focal length of such a unit is so short as to provide a widerelative aperture for the optical unit, certain interference efiectshave been noted. These interference effects have been the subject matterof investigation by eminent physicists, and are perceptible as to thoserays which converge at points removed from the axis of the unit. Theseinterference effects improve the resolving power by destroying the outerportion of the diffraction pattern.

It is one of the objects of this invention to make it possible toimprove the optical performance of such units, causing the unit to havehigh resolving power and to produce a more brilliant image.

In order to accomplish these results, a very thin optical wedge isformed over the optical surface, and arranged so as to alter the lengthof the optical path, by values always considerable less than the averageWave length of light; and even less than half of such wave length. Thewedge obviously must be extremely thin to fulfill this requirement. Theoptical wedge is such that its thickness is a function of the positionof a generatrix revolved about the axis of the unit. Inother words,assuming that a section is made of the optical wedge along a cylinderhaving its axis coincident with the axi of the unit, then the thicknessof the Wedge along such a section is a continuous function of the angleof the radius of the cylinder.

In addition, the thickness of the wedge along a section passing throughthe axis, also varies with the radial distance of the point of the wedgefrom the axis. I

The theoretical considerations upon which the improved optical resultsare secured by such a wedge in conjunction with the optical unit arecomplex, and need not be detailed herein. The Wedge may be refracting orreflecting, depending upon the character of the optical unit.

It is still another object of this invention to provide a simple andinexpensive process for depositing wedges of this character upon theoptical unit.

This invention possesses many other advantage and has other objectswhich may be made more easily apparent from a consideration of severalembodiments of the invention. For this purpose there are shown a fewforms in the drawings accompanying and forming part of the presentspecification. These forms will now be described in detail, illustratingthe general principles of the invention; but it is to be understood thatthis detailed description is not to be taken in a limiting sense, sincethe scope of the invention is best defined by the appended claims.

Referring to the drawings:

Figure 1 is a, pictorial view of an optical unit produced by theprocess, one of the dimensions being greatly exaggerated for the sake ofclarity;

Fig. 2 is a sectional view taken along plane 22 of Fig. 1;

Fig. 3 is a sectional view similar to Fig. 2, of a modified form of theoptical unit;

Fig. 4 is a sectional view similar to Fig. 2 of a further modified formof the optical unit;

Fig. 5 is a development of a section taken along a cylindrical surface55 of Fig. 1;

Fig. 6 is a diagrammatic view of apparatus utilized in connection withthe process of forming the optical units illustrated in Figs. 1, 2, 3and 4, and

Figs. 7, 8 and 9 are plan views of various forms of shutters that may beutilized in connection with the apparatus illustrated in Fig. 6.

In the form illustrated in Figs. 1 and 2, the

optical unit is shown as a concave lens or mirror l. The unit is builtup by the depositing of a supplemental layer 2 over a true surface ofrevolution 3, which may be formed by a generatrix rotated about the axis4 of the unit. This supplemental layer 2, if the unit I is a lens, isformed of transparent material such as quartz or the like. The depositmay be secured by subjecting the surface of revolution 3 to a stream ofvaporized material to be deposited.

The depth of the layer 2 is shown very greatly exaggerated. This depthis such that the difference between the maximum and minimum depths ofthe entire layer is such as to correspond to a change of optical path ofnot more than one average wave-length of light; and in some instancesthis difference in the optical path may be les than one-half such wavelength.

The nature of the layer 2 is such that its thickness varies continuouslyfor different angular positions of the intersecting plane which passesthrough the axis 4. If we consider plane 2-2 as a beginning position,then as this plane moves angularly in a counterclockwise direction, thethickness gradually increases until the intersecting plane again arrivesat the beginning position. Since the thickness of the deposit increasesfrom the beginning to the ending position, an abrupt step ordiscontinuity is formed, defined by the lines 5 and 6. The step betweenlines 5 and 6 corresponds to the maximum thickness of the layer. Thismaximum thickness represents the thick end of a circular wedge extendingaround the surface of revolution 3. V

The effect of a supplemental layer is therefore that of an optical wedgehaving its thin and thick edges in a common plane radial to the axis 4and passing through it. The thickness of the wedge increases graduallyin a counterclockwise direction from the beginning position.

This effect is shown most clearly in Fig. 5, which is the development ofthe cylindrical section taken along the cylindrical surface 45 indicatedin Fig. 1. The minimum thickness at edge I is shown as at one extremityof the layer 2. The maximum thickness 8 of the layer 2 is shown at theopposite end of the figure.

Although in this form, the thickness of the layer 2 is uniform for anyplane of the section, from the axis to the outer edge of the unit I, itmaybe advisable to vary as well the thickness of the layer from the axisto the edge of the unit. Such a variation is illustrated in Fig. 3. Inthis case, the optical unit I has superposed thereon a supplementallayer 9. The thickness of this layer gradually increases from the axis 4to the edge of the unit, in any plane of the section.

In the event that the optical unit is a reflector, then the supplementallayer 2 or 9 may be in the form of sputtered metal that forms a mirrordeposit upon the unit.

The unit i is shown in the present instance as having a concave opticalsurface. In the form illustrated in Fig. 4 the unit In is provided witha convex optical surface ll, again formed as a true surface ofrevolution about the axis 12. The supplemental layer 13 is of the samecharacter as illustrated in the previous forms described. In alltheselayers the maximum difference in optical path from the thinnest to thethickest part is substantially less than the average wave length oflight, and preferably in some instances it may be less than one-half theaverage wave length of light. 7

These extremely thin wedges thus superimposed upon true surfaces ofrevolution may be conveniently obtained by the aid of the novel processdisclosed by the aid of Fig. 6.

Inthat figure an evacuated space M is indicated including a stationarymetallic base member l5 and a bell-like cover l6. An exhaust pump may bein continual operation for maintaining the space M at a sufiicient lowpressure. The optical unit I! to be treated is shown as appropriatelysupported so that its axis is coincident with an axis l8 and with itsoptical surface i9 directed downwardly. This optical surface 19 issubjected to a stream 29 of finely divided material, emanating from areceptacle 2! located within the space M. This material may be in theform of vaporized quartz or vaporized metal, heated as by an electriccurrent. For example, a heating coil 22 may be utilized, in good heatconducting relation to the material to be vaporized that is locatedwithin the receptacle 2|. The manner in which electrical energy is fedto the unit 2| will be described hereinafter.

The receptacle 2| is shown as carried by an arm 23 having a hub 24. Thishub 24 is insulatingly supported upon a shaft 25 which projects out ofthe chamber (4. This shaft 25 is in turn insulated from a rotatableconical plug member 26 passing through an appropriate hub 21 in thebottom of the base IS. The axis of the shaft 25 is coincident with theaxis l8 of the unit H.

The lower edge of the plug 26 may be formed as a worm gear 28 adapted tobe driven as by a worm 29. This worm 29 is shown diagrammatically asbeing operated by an adjustable speed device 39.

The shaft 25 is insulated from the rotatable plug 26, and can thereforebe used as a connection for the electric heating unit 22. For thispurpose one terminal of the heating unit is joined to the shaft 25 andits other terminal may be grounded upon the arm 23. A source ofelectricity, such as the battery 3|, has one terminal connected to theboss 21 and its other terminal is connected by a brush 32 to the lowerend of the shaft 25. The energy delivered by the battery 3| is such asefiectively to vaporize the material in the receptacle 2|. As the sourceof motion 30 rotates the receptacle 21, the stream of vaporizedparticles 29 is directed against the optical surface l9. s

In order to regulate the area where vaporized material is deposited, ashield 33 is interposed between the receptacle 2| and the surface [9.This shield 33 may be in the form of a disk appropriately fastened tothe upper end of the shaft 25. It is provided with a slit or opening 34(shown in greater detail in Fig. 7) through which the stream 29 passes.As the shaft 25 is rotated through the medium of the plug 26, the gear28- and the worm 29, the slit 34 remains in a proper operativerelationship with the receptacle 2]. By appropriate configuration of theslit 34, the thickness of the deposit formed upon the optical surface l9may be regulated. The thickness from point to point of this layer may befurther controlled by appropriate adjustment of the speed of themechanism 39; thisadjustment may be in the form of a continuousvariation repeated cyclically for repeated revolutions of the shaft 25.

Thus if the slit 34 is of the form illustrated in Fig. 7, it is clearthat a greater depth of the vaporized particles will be deposited nearerthe edge than nearer the center of the optical unit 11. The radialextent of the slit 34 is furthermore so chosen that the stream 20 isquite well confined to extend no further than from the axis l8 to theouter edge of the unit II.

By appropriate choice of the shape of the slit- 34, different thicknesseffects may be obtained. A few of such variations are illustrated inFigs. 8 and 9.

In Fig. 8 the slit 35 in the shield 36 is so ar-- ranged that a thickerdeposit is formed adjacent the axis of the unit. In Fig. 9, the slit 31in the shield 38 is so arranged as to ensure a considerably heavierdeposit adjacent the edges of the unit l1. g

If the speed of the-mechanism 39 is varied continuously throughout eachrevolution, the amount of material deposited at any small area of theunit is proportional to the time of transit of the slit across theparticular portion of the unit. Some control of the depth of the depositis also 5 obtained by the appropriate choice of the form of slitutilized.

The inventor claims:

1. The process of forming a thin layer on an optical surface having anaxis, said layer having a wedge-like cross section in a directionextending about the axis, which comprises: finely di viding materialthat is capable of adhering to the surface, passing the finely dividedmaterial through a slot or opening so as to impinge on said surface,rotating said slot or opening about said axis, and varying the rate ofrotation through each revolution to obtain a non-symmetricaldistribution of the material about said axis.

2. The process of forming a thin wedge-like layer on an optical surface,which comprises: vaporizing the material to be deposited, passing thevaporized material through an opening having a REFERENCES CITED Thefollowing references are of record in the file of this patent:

UNITED STATES PATENTS 15 Number Name Date 2,259,395 Sachtleben Oct. 14,1941 2,160,981 OBrien June 6, 1939 2,153,363

Bruche Apr. 4, 1939

